The invention is related to the field of semiconductor fabrication and more particularly to a method for incorporating nitrogen into a dielectric layer.
In the field of semiconductor fabrication, boron penetration from p-type polysilicon into the transistor channel region is a well-known problem in CMOS processes. The presence of boron in the transistor channel can act as a counter dopant in a PMOS transistor, thereby undesirably altering the threshold voltage of the P-channel transistors. Manufacturers have addressed this boron penetration problem in a variety of methods including introducing nitrogen into the transistor gate dielectric. The presence of nitrogen in the gate dielectric is believed to significantly retard the ability of impurities such as boron to migrate. Nitrogen has been introduced into the bulk of the dielectric layer itself and at the interface between the dielectric and the underlying silicon substrate. Introducing nitrogen at the silicon-dielectric interface is known to increase the interface state density (Dit) thereby causing degradation in device performance. Thus, it is preferable to introduce nitrogen into the bulk of the dielectric itself. Introducing nitrogen into the dielectric bulk, however, is difficult to implement in processes using high-K dielectric layers such as metal oxides. The use of a remote nitrogen plasma has been proposed to facilitate the introduction of nitrogen into the dielectric layer with a chemical vapor deposition (CVD) process. Typically, multiple precursors are required to implement this CVD process. In addition to introducing process complexities, multiple precursor processes require a highly reactive process to form the necessary metal-oxygen nitrogen bond. To achieve sufficient reactivity, it is typically necessary although undesirable to increase the deposition temperature or power (in the case of a plasma process). In addition, it is generally more difficult to maintain control of a multiple precursor process in a manufacturing environment. Therefore, it would be desirable to implement a process for forming a nitrogen bearing high-K dielectric using a single precursor that contains a metal-oxygen-nitrogen moiety.